Cathodes for electrical discharge devices



Dec. 18, 1956 H. KATz y 2,774,916

CATHODES ECR ELECTRICAL DISCHARGE DEVICES Filed June 9, 1952 OQQQQQQOQQID United States Patent O CATHODES FOR ELECTRICAL DISCHARGE DEVICES Helmut Katz, Erlangen, Germany, assignor to Siemens &

Halske Aktiengesellschaft, Munich and Berlin, Germany, a German corporation Application June 9, 1952, Serial No. 292,433 Claims priority, application Germany June 9, 1951 Claims. (Cl. 315-94) This invention relates to a cathode for use in electrical discharge devices, especially a cathode of the type having a receptacle containing a supply of an emissive material which is covered by a cathode body and migrates at operating temperature through line passages of such cathode body to the emitting surface formed thereby, and is particularly concerned with the provision in such a cathode of a heater disposed in insulated relationship relative to the cathode body, said heater being adapted to give olf electrons, the electron stream occurring responsive to the connection of a potential between the cathode and the heater being utilized to heat the cathode to emission temperature or to contribute decisively toward heating it to emission temperature.

Cathodes of the type having a supply of an emissive material, which migrates at operating temperature to the cathode surface, have been proposed before. The fine passages for the migration of such material may be formed by wire or the like tightly wound about ,the cathode body, or they may be formed by the pores of a sintered body made of a substance upon which they emissive material can migrate. Tungsten and molybdenum have been found particularly suitable for cases in which thorium or barium compositions are employed as emissive materials.

The advantages flowing from the invention reside in the decoupling between the cathode and the heater and in the possibility of dosing or regulating the cathode temperature within widest limits by placing dierentiating voltages on the circuit between the cathode and the heater. This is of importance because it is decisive to provide for certain amounts of emissive material upon the cathode surface in accordance with varying conditions that occur in the operation of discharge devices. It may happen e. g., in the case of cathodes employing barium or thorium as an emissive material that the reduction or vaporization velocity of these substances does not have the required value at the emission temperature of the cathode surface. If the velocity is too great, there will be produced a wasteful excess of the emissive material, impairing the life of the cathode; if it is insuiiicient, there will not be optimal spreading of the material on the cathode surface, and the temperature will have to be raised. There will be in either case waste and ineicient operation.

The invention avoids these drawbacks by easy and efiicient regulation of the cathode temperature through the adjustment of the electron bombardment.

Care is taken by the decoupling between the heater and the cathode to avoid electrons emanating from the heater from reaching the electron stream emitted by the cathode.

Depending on the desired Working conditions, it is possible to operate selectively with voltages between the heater and the cathode which may go down to zero. This feature is of significance in the manufacturing of discharge devices and also useful in the operation thereof, because it is often desirable to use for quick heating high cathode temperatures. Higher voltages are for such pur- 23,774,916 Patented Dec. 18, 1956 lCe pose connected between heater and cathode which may subsequently be switched olf.

The invention also permits automatic regulation of the emission in the case of variable cathode loading. The voltage between cathode and heater may by suitable and known means be increased at times when greater cathode loading is required. The voltage may be disconnected for inoperative periods, so that the heating of the cathode is solely effected by heat conduction or radiation of the heater. v

The invention will be explained with reference to the accompanying drawings, wherein Fig. l shows, in simplilied schematic manner, the essential elements of a llat cathode; and

Fig. 2 indicates in like manner a modified at or disklike cathode.

Identical references indicate identical parts.

The cathode shown in Fig. l comprises a flat or disklike porous sintered body 1 made of tungsten or molybdenum, forming the cathode emission surface. This body is intimately connected, by welding or the like, with a receptacle 2 in which is disposed an emission material 3, for example, thorium or a thorium compound. Barium or barium compounds may be used depending upon the purpose for which a tube provided with the cathode is to be used. Numeral 4 indicates a retainer which is intimately connected by welding or the like, with the receptacle 2 and the cathode body 1. In the annular space between the retainer 4 and the receptacle 2 is disposed a heater clement 5. The heater element 5 is supplied with current from the secondary winding 6 of a transformer having a primary winding 7 which is connected to an alternating current source 8. A direct current source 9 lsupplies negative potential to the heater element 5 over a potentiometer 10. The wall of the receptacle is connected to the positive terminal of the direct current source 9. Responsive to reaching operating temperature due to current from the secondary transformer winding 6, the heater element 5 will emit electrons, the wall of the receptacle 2 acting in the manner of an anode, the emission being regulable yby means of the potentiometer 10. The innermost turn of the heater element 5 is disposed close to the cathode body 1 while all turns are spaced from the wall of the receptacle 2. Accordingly, the cathode body 1 will be heated primarily by the heat from the heater element while less heat is supplied therefrom to the receptacle 2 containing the emission material 3. Such receptacle and the emissive material therein will be primarily heated, if desired periodically, by electron bombardment from the heater element 5.

The embodiment shown in Fig. 2 is similar to Fig. l. It comprises a flat or disklike sintered body 1 forming the cathode emission surface as before. This body is intimately connected with wall means 1S, 16, 17, forming a receptacle containing a supply of emission material 3. Numeral 4 indicates a retainer such as is also used in Fig. 1. A heater element 18 is disposed close to the cathode body 1. The heater element 18 receives current from the secondary winding 6 of the transformer which has its primary winding 7 connected to an alternating current source 8, all as in the embodiment according to Fig. l. The circuit connections for effecting electron bombardment correspond to those explained with reference to Fig. l. The heat produced by the electron bombardment will beprimarily effective to the cathode body 1.

It will be seen, therefore, that the invention provides for different and selectively controllable heat transfer to the cathode body and to the receptacle containing the emission material. The intensity of the electron bombardment is regulable by the potentiometer 10 in accordance with desired electron emission from the heater element. Waste and inefficient operation may be avoided by regulating the electron bombardment to regulate respectively the temperature of the cathode body 1 (Fig. 2) or of the receptacle 2 (Fig. 1) containing the emission material.

It is understood, of course, that the conductors shown in Figs. 1 and 2, for supplying current to the various parts, are carried to the outside of the tube envelope. The latter and also other parts of the tube have been omitted in order to avoid encumbering the drawing with known structure that does not form part of the invention.

The electron bombardment desired and intended by the invention may be obtained by the use of direct or alternating current in a circuit between the heater and the cathode. Rectitiers may be used in the case of alternating current so as to cause the heater to operate as a cathode. It is, however, also possible to operate purely with alternating current, particularly in cases where the wall surfaces of the cathode facing the heaterdo not at operating temperature exhibit any noticeable electron emission. High frequency alternating current may likewise be used.

The structures shown in Figs. 1 and 2 need not be circular. They may be rectangular or striplike. The term dat is intended to embrace all such variations in shape.

Changes may be made within the scope and spirit of the following claims.

I claim:

l. In an indirectly heated dispenser type cathode comprising a receptacle element containing a supply of emission material and an emissive element connected therewith through which emission material from said supply can migrate in operation to a surface formed thereby, said surface constituting the cathode emitting surface, and having an insulated heater and a current source for' heating it so as to transfer heat to both said elements for the purpose of heating them to effect migration of emission material from said supply to said emitting surface; a device for selectively regulating the temperature of one of said elements independent of the temperature imparted thereto by heat from said heater for the purpose of providing optimum emission of emission material at said emitting surface, said device comprising a source of direct current, circuit means for connecting current from said source to said receptacle element and to said heater so as to cause said heater to emit an electron stream impinging primarily upon said one element, thereby supplying auxiliary heat to such element, and a potentiometer included in said circuit means for regulating electron emission from said heater to regulate the supply of auxiliary heat to said one element.

2. An arrangement and cooperation of parts according to claim l, wherein said emissive element is said one element upon which said electron stream emanating from said heater impinges primarily so as to supply auxiliary heat thereto.

3. An arrangement and cooperation or parts according to claim- 1, wherein said receptacle element is the one element upon which said electron stream emanating from said heater impinges primarily so as to supply auxiliary heat thereto.

4. An arrangement and cooperation of parts according to claim l, wherein said emissive element is a flat disklike element, a spirally coiled insulated wire disposed in a plane extending in parallel relatively closely adjacent said disklike emissive element, said wire constituting said heater, said ilat disklike emissive element constituting said one element upon which said electron stream emanating from said heater impinges primarily so as to supply auxiliary heat thereto.

5. An arrangement and cooperation of parts according to claim 1, wherein said emissive element is a flat disklike element, a helically coiled insulated wire extending axially in a direction perpendicular to the plane of said emissive element, said wire constituting said heater, said receptacle element having a wall extending coaxially with said heater, said receptacle element being said one element upon which said electron stream impinges primarily so as to supply auxiliary heat thereto.

References Cited in the le of this patent UNITED STATES PATENTS 1,699,146 Hull Jan. l5, 1929 1,864,591 Foster June 28, 1932 2,121,589 Espe June 21, 1938 2,392,397 Litton Jan. S, 1946 2,543,728 Lemmens et al Feb. 27, 1951 2,552,047 Kurshan May 8, 1951 OTHER REFERENCES Lemmens: Jansen and Loosjes, A New Thermionic Cathode for Heavy Loads, reprint from Philips Technical Review, vol. 11, No. 12, pp. 341-350, June 1950. 

